Get dealer to VIN-dicate problem with downshifting

Q: My 2009 Hyundai Sonata has an ongoing shifting problem. When I am slowing and the speedometer is crossing the 20-mile-per-hour mark, it “surges” as though I can feel the downshift. First we tried a transmission fluid flush, but that did not help. A second mechanic said it is just the way the car is and there is nothing functionally wrong. What do you think?

Hyundai has issued several programming updates for the ECM and TCM to address these issues. I’d suggest having your dealer check the VIN of your car to see if any of these updates have been done. If not, a scan tool might pull up specific DTC fault codes and the updated programming may smooth out the downshifts.

Q: I have a 1999 Mercury Grand Marquis 4.6-liter with 135,000 miles. It has a Gold Diehard battery that is about a year and a half old. On cold starts, no problems, but if I drive several miles and then turn the car off for a few minutes to an hour, when I start it the battery light comes on. After a few miles or a few minutes, it goes off. The battery and alternator test fine with my multimeter, but I can’t re-create the “light on” scenario in the garage while testing. It just comes on at start-up and then goes off.

A: By definition, the battery warning light illuminates when system voltage does not increase above battery voltage, indicating that the charging system isn’t recharging the battery. When the engine is started, the alternator’s “field” circuit must be electrically energized with battery voltage to create the magnetic field necessary to generate current.

On a restart where the “batt” light stays illuminated, try leaving the car in park and gently raising the engine rpm to 2,000 or so. If the warning light goes off, it means the voltage regulator built into the alternator has recognized the need to charge the battery.

With the key on but the engine not running, check fuse 3 (5-amp) and the “gen” fuse (10-amp) in the power distribution block to make sure they’re clean with solid connections, and check for battery voltage at the “F” (field) terminal on the back of the alternator.

Keep an eye out for a good deal on an alternator; you might need a new one in the near future.

Q: I own a 2005 9-2 Saab. It is due for new brake rotors. I understood there are four main types of replacement rotors on the market: flat (the usual OEM rotors), drilled, slotted and the combination of both. I’m looking to increase stopping power and reduce stopping distance while keeping the rotors from warping. Is there really a benefit to any these aftermarket rotors?

A: The different styles of rotors won’t really affect stopping “power” or distance. As long as the brakes have the “power” to lock the wheels and tires, it’s the tires that influence stopping distance the most. Better stopping power would require larger brakes and higher-grip tires. Look at it this way: Brakes are engines that work in reverse, so to speak. Brakes convert the energy of motion into heat. The bigger the brake, the more efficient the engine.

Slotted, drilled and vented rotors do offer one major advantage — they dissipate heat better, thus allowing more frequent and harder braking without overheating/fading/warping in high-performance and racing applications.

In your case, higher-performance brake pads would have a greater influence on stopping power than different style rotors.